Flights to Sofia

These are some airlines that fly directly USA (SF, NY, LA, CHI, Seattle) <--> Europe and Europe <--> Sofia

Air France: USA <--> Paris <--> Sofia
Alitalia: USA <--> Milan <--> Sofia (Italian airlines)
British Airlines: USA <--> London/Manchester <--> Sofia
Check Airlines: USA <--> Prague <--> Sofia
KLM: USA <--> Amsterdam <--> Sofia (Dutch airlines)
LOT: USA <--> Warsaw <--> Sofia (Polish airlines)
Lufthansa: USA <--> Frankfurt/Munich <--> Sofia
MALEV: USA <--> Budapest <--> Sofia (Hungarian Airlines)

Most of these companies have one-two flights to/from Sofia per day. Note that some of them (Check airlines, LOT, MALEV) might try to attract you by offering one night in resp. Prague, Warsaw and Budapest almost free of charge.